1. Field of the Invention
This invention relates to a UV detector having a novel structure and UV intensity and dose measuring method using the same.
2. Description of the Related Art
In recent years, UV or short wavelength lights have been utilized industrially in various fields. Particularly, UV has been utilized vigorously to improve resolutions upon exposure in production steps of semiconductor integrated circuit devices. Along with super micro miniaturization of semiconductor integrated circuit devices in recent years, light sources of UV used in photo-lithographic steps by demagnification optical systems of production steps have been shifted from mercury lamps (365 nm) to excimer lasers of a shorter length such as KrF (248 nm) or ArF (193 nm). As described above, when lights (also including UV or shorter wavelength lights) are utilized industrially, a technique of accurately measuring the intensities of such lights has been required.
Further, effects of UV in sunlight on human bodies have brought about a significant problem and the requirement for the technique of accurately measuring the UV-intensity and dose has increased more.
Heretofore, for measurement of UV intensity, apparatuses having a combination of a panchromatic detector such as a silicon photodiode with a long wavelength cut-off/short wavelength transmitting filter and a long wavelength cut-off/short wavelength transmitting filter for cutting-off secondary light transmission in the visible region of the filter have been used as UV detectors. However, such cut-off filters involve problems that it is difficult to obtain a favorable combination, sensitivity to UV is lowered by superimposing the filters and, further, they show large errors with transmitting visible light or significant aging change due to deterioration of filter, and the working life is short.
In addition, the silicon photodiode involves a problem that light does not reach an active portion due to surface absorption in a case of measuring light at short wavelength, or the sensitivity is lowered at a wavelength of 400 nm or less, for example, by recombination due to surface defects. Further, it also involves a problem that the sensitivity fluctuates greatly depending on the wavelength at 300 nm or less, so that no accurate light or intensity and dose can be determined.
For the measurement of UV intensity, a UV detector including a semiconductor having sensitivity to short wavelength such as GaP with a long wavelength cut-off/short wavelength transmitting filter is also used. Also in this case, since the receptor has a sensitivity to a secondary light region in a case of UV at 300 nm or less, it is necessary for a short wavelength transmitting/long wavelength cut-off filter for cutting-off the secondary light transmitting area. Such a cut-off filter is expensive since the material constituting the cut-off filter for transmitting the light in the short wavelength region is limited. As a result, the UV detector in such a region has a short life and low sensitivity while it is expensive.
For the short wavelength transmitting filter as described above, since the angle dependence of the filter is large for obtaining aimed UV, the deflection for the incident angle has to be reduced as much as possible for accurate measurement of intensity and dose in the aimed wavelength region and, ideally, vertical incidence of light is desired. Then, the length of the light guide portion to the receptor has to be increased inevitably in order to keep the optical channel vertical and the length increases as the accuracy of the receptor is higher to result in a problem that the size of the photoreceptor is enlarged.
Further, in UV detectors, for accurately measuring the intensity of UV, it is necessary to use a photo-receiving device conforming to the so-called cosxcex8 rule for the distribution of the incident angle for measurement of UV from all directions. As an ideal UV detector, it is desirable to use a photo-receiving device which is reduced in size and conforms to the cosxcex8 rule as much as possible. However, in the photo-receiving device conforming to the cosxcex8 rule up to about an angle of 60xc2x0, the thickness is limited to 8 to 10 min (data reported in Illumination Society). Accordingly, the extent for the distribution of the incident angle for measurement and the thickness of the photo-receiving device conflict with each other.
Meanwhile, the UV detector is adapted to measure the UV intensity and dose on an object while being in contact or adjacent with the object. In a case of a UV detector using a transparent nitride semiconductor, incident light at a portion of a long wavelength that is transmitted while undergoing attenuation by absorption of the nitride semiconductor reflects on the surface of the object and then enters again to the nitride semiconductor and, as a result, a problem arises that the spectral characteristic and the output are changed. Particularly, the amount of change increases depending on the color of the object, and accurate measurement for the UV intensity and dose is difficult. Specifically, in a case for example, where a UV detector is used while it is disposed on humans skin, the spectral sensitivity characteristic and the output are changed due to the difference of the color of skin.
This invention has been made in view of the above circumstances and provides a UV detector capable of accurately measuring the UV intensity for a wide incident angle with no change of the spectral sensitivity characteristic or output, irrespective of a color of an object on which the UV intensity and dose measurement is carried out, as well as a method of measuring the UV intensity and dose using the same.
That is, this invention provides a UV detector which is located at an arbitrary measuring position on an object and measures UV intensity and dose at the measuring position. The UV detector includes a UV receiving device having a photosemiconductive layer containing at least one of elements of Al, Ga and In, and nitrogen, and a UV untransmissive member having a function of preventing UV which is transmitted through the UV receiving device from being received by the object.
Further, this invention provides a method of measuring UV intensity and dose by using the UV detector described above, wherein the UV detector is located at an arbitrary measuring position on an object and the UV intensity and dose at the measuring position is measured.